1. Field of the Invention
The present invention relates to a process for oxidizing an organic compound such as naphthalene by means of a ceric sulfate-aqueous sulfuric acid solution, to obtain an oxidation product of the organic compound such as 1,4-naphthoquinone industrially advantageously.
2. Discussion of the Background
It is well known to oxidize an organic compound such as naphthalene by means of an aqueous acid solution of a ceric compound. For instance, as industrial processes, there may be mentioned (1) a process wherein a polynulear aromatic hydrocarbon dissolved in a water-immiscible organic solvent, is oxidized by means of a ceric salt-aqueous acid solution such as a ceric sulfate-aqueous sulfuric acid solution to obtain a quinone corresponding to the polynuclear aromatic hydrocarbon (Japanese Examined Patent Publication No. 34978/1974), (2) a process wherein powdery naphthalene is reacted while it is suspended in an aqueous solution of a ceric salt by means of a dispersing agent (Japanese Unexamined Patent Publication No. 61321/1981), and (3) other processes such as a process for producing from toluene or its substituted derivative a corresponding benzaldehyde, and a process for producing from a secondary alcohol a corresponding ketone [Walters Trahanovsky et al., J. Chem. Soc., 1966, pages 5777-5778; Koichiro Ohshima, Journal of Organic Synthetic Chemistry Association, 40(12), pages 1171-1179 (1982)]. As the ceric compound-aqueous acid solution to be used for the oxidation reaction in these processes, it is particularly advantageous from the industrial point of view to employ a ceric sulfate-aqueous sulfuric acid solution which has relatively low corrosiveness, contains little by-products, and is industrially readily available at low cost, taking into consideration a step of electrochemical regeneration which is commonly employed as a method for regenerating the resulting cerous salt into the ceric salt, after the oxidation reaction.
However, the conventional oxidation reaction with use of a ceric compound is usually conducted at a concentration lower than the maximum solubility of the cerium compound. For instance, the ceric sulfate concentration in a ceric sulfate-aqueous sulfuric acid solution used to be limited to a low level of from 0.25 to 0.278 mol/liter, since the solubility of cerous sulfate resulting from the oxidation reaction with the ceric sulfate is relatively small. In addition, when the cerous sulfate resulting from the oxidation reaction is to be regenerated as ceric sulfate by electrochemical oxidation, the current efficiency is largely dependent on the concentration of cerous sulfate as shown in FIG. 4, according to the experimental results by the present inventors. Therefore, when electrolysis cost constitute a substantial portion of the price of the product, a predetermined amount of cerous sulfate will remain in the regenerated ceric sulfate solution in order to increase the current efficiency. When cerous sulfate remains, the effective amount per unit volume of ceric sulfate used in the respective reactions in the conventional processes, will decrease, and it will be necessary to enlarge the reactor and the accompanying installations, thus leading to industrial difficulties. The industrial application of the method for the oxidation of an organic compound by means of a ceric sulfate-aqueous sulfuric acid solution has been prevented by such industrial difficulties inherent to the conventional processes.